The present invention relates to an organic electroluminescent (hereinafter abbreviated as xe2x80x9cELxe2x80x9d) array exposure head and a method of fabricating the same and also pertains to an image forming apparatus using the same. More particularly, the present invention relates to an organic EL array exposure head integrated with image-forming lenses and a method of fabricating the same and also pertains to an image forming apparatus using the same.
Various techniques of using an organic EL array as an exposure head for image forming apparatus have heretofore been proposed. Those concerned therewith are as follows.
In Japanese Patent Application Unexamined Publication Number [hereinafter referred to as xe2x80x9cJP(A)xe2x80x9d] Hei 10-55890, the whole organic EL array is fabricated on an insulating substrate, e.g. glass, and a separate driver IC is combined with the organic EL array. A converging rod lens array is used to image the light-emitting parts of the organic EL array onto a photosensitive drum.
JP(A) Hei 11-198433 uses a one-chip organic EL array having a plurality of rows of light-emitting parts. However, the optical system for imaging the light-emitting parts onto a photosensitive drum is not clear. It should be noted that an EL layer of the organic EL array is deposited by evaporation.
In JP(A) 2000-77188, microlenses are formed on the top surface of a substrate by an ion exchange method. Alternatively, microlenses are formed on the bottom surface of a substrate by a method using a photoresist or by a replica method. An organic EL array having a resonator structure is deposited in alignment with the microlenses by evaporation.
JP(A) Hei 10-12377 relates to a method of producing an active matrix organic EL display. An organic light-emitting layer is formed by ink-jet printing over a glass substrate having thin-film transistors.
In JP(A) 2000-323276, a hole injection layer and an organic light-emitting layer of an organic EL element are formed by coating using ink-jet printing with a partition wall provided therearound.
In JP(A) 2001-18441, a light-emitting layer and a TFT layer for controlling light emission therefrom are formed in a photosensitive drum to construct a printer.
When an organic EL array is used as an exposure head of a printer, e.g. an electrophotographic printer, in the above-described prior art, JP(A) Hei 10-55890 and Hei 11-198433 need to use a separate optical system. This causes the apparatus to increase in size and cost unavoidably. JP(A) 2000-77188, in which the organic EL array is integrated with microlenses, suffers problems such as a restriction in usable microlens materials. Further, these conventional techniques involve problems such as a narrow selectivity of materials for the EL layer because it is formed by evaporation.
The present invention was made in view of the above-described problems with the prior art.
An object of the present invention is to provide an organic EL array exposure head integrated with microlenses for converging or diverging light from light-emitting parts, together with a method of fabricating the organic EL array exposure head and an image forming apparatus using the same.
To attain the above-described object, the present invention provides an organic EL array exposure head including an array of organic EL light-emitting parts arranged in the form of at least one row of pixels on a substrate of continuous length. The organic EL array exposure head further includes a microlens formed by ink-jet printing over a surface of each organic EL light-emitting part at a side thereof remote from the substrate.
In this case, it is desirable that the organic EL light-emitting parts should be formed in respective discrete holes divided from each other by a partition wall provided on the substrate, and the microlens should be formed over each of the organic EL light-emitting parts in the holes.
It is also desirable that a thin-film electronic circuit for controlling light emission from the organic EL light-emitting parts should be formed on the substrate, and the organic EL light-emitting parts should be provided over the thin-film electronic circuit.
An organic light-emitting layer and a hole injection layer constituting the organic EL light-emitting parts may also be formed by ink-jet printing.
It is desirable that the microlens should be a convex lens.
In addition, the present invention provides a method of fabricating an organic EL array exposure head. According to the fabrication method, reflector electrodes are formed in the form of at least one row of pixels on a substrate of continuous length. Each reflector electrode constitutes one electrode of each organic EL light-emitting part.
Then, a partition wall of a predetermined height is formed over the reflector electrodes. The partition wall has discrete holes corresponding to the reflector electrodes. Then, an organic light-emitting layer or a hole injection layer constituting each organic EL light-emitting part is formed in each hole in the partition wall by ink-jet printing.
Then, a hole injection layer or an organic light-emitting layer constituting each organic EL light-emitting part is formed in each hole in the partition wall by ink-jet printing.
Then, a transparent electrode is formed uniformly over a surface of the substrate as the other electrode of each organic EL light-emitting part.
Thereafter, a microlens is formed over the transparent electrode in each hole in the partition wall by ink-jet printing.
In this case, after the formation of the transparent electrode, a surface thereof may be treated to be water repellent so that a convex lens is formed thereon as a microlens. Alternatively, the surface of the transparent electrode may be treated to be hydrophilic so that a concave lens is formed thereon as a microlens.
It is desirable that prior to the formation of the reflector electrodes, a thin-film electronic circuit for controlling light emission from the organic EL light-emitting parts should be formed on the substrate.
The present invention includes image forming apparatus having the above-described organic EL array exposure head as an exposure head for writing an image on an image carrier. One example is a tandem color image forming apparatus including at least two image forming stations each having an electric charging device, an exposure head, a developing device, and a transfer device around an image carrier, wherein a transfer medium passes through the stations to perform color image formation.
Thus, the organic EL array exposure head according to the present invention has an array of organic EL light-emitting parts arranged in the form of at least one row of pixels on a substrate of continuous length. The organic EL array exposure head further has a microlens formed by ink-jet printing over a surface of each organic EL light-emitting part at a side thereof remote from the substrate. Accordingly, it is possible to readily provide a low-cost exposure head for use in electrophotographic printers, etc. that suffers minimal unevenness of exposure and has a simplified arrangement requiring no separate optical system.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.